The present invention relates to semiconductor doping compositions and more particularly to semiconductor doping compositions that may be spun onto a semiconductor substrate and used in integrated circuit manufacture. The semiconductor doping composition comprises a suspension of
(a) a dopant material, in the form of finely divided spherical particles of narrow size distribution from about 0.1D to D, where D is the diameter of the largest particle and is no more than about 1.mu. comprising a member selected from the group consisting of B.sub.x Si.sub.y, B.sub.x N.sub.y, P.sub.x Si.sub.y, P.sub.x N.sub.y, As.sub.x Si.sub.y and Sb.sub.x Si.sub.y wherein x and y vary from about 0.001 to about 99.999 mole percent,
(b) an effective amount of a thermally degradable polymeric organic binder such as polymethyl methacrylate; and
(c) an amount of an organic solvent, such a cyclohexanone, sufficient to dissolve said polymeric organic binder and to disperse said dopant material
Methods are known for making junction-type semiconductor devices (transistors, diodes, etc.) that involve the introduction, into a semiconductor substrate or suitable wafer material such as silicon, germanium, gallium arsenide, gallium phosphide, indium antimonide, or silicon-germanium alloy, of a controlled, small quantity of a dopant. For silicon, there are known N-type dopants, such as phosphorus, arsenic, and antimony; and there are known P-type dopants, such as boron, indium, aluminum, and gallium.
Since the junction depth of the dopant and the surface dopant concentration must be uniform to produce high yields of junction-type semiconductor devices having uniformly high service characteristics, a number of dopant compositions and processes to diffuse the dopants into the semiconductor materials are known. For example, D. Rupprecht et al. (J. Electrochems. Soc. 1973, Vol. 120 1266-1271) disclose that boron nitride wafers are oxidized in a diffusion furnace to B.sub.2 O.sub.3 or HBO.sub.2, and the oxide is transferred in the vapor phase to the silicon wafer surface or boric oxide wafers can be used directly. However, boron oxide and related sources are usually sensitive to moisture, create damaged or stained silicon surfaces, and/or involve costly and complicated processes to achieve quality doping. In addition, these dopant materials, as prepared by prior art methods, usually contained metal ion impurities, Na, Fe or Co which interfered with the operation of semiconductor devices manufactured with these impure dopant materials.
The prior art also discloses doping by means of liquid doping compositions which include a variety of organic and inorganic slurries, mixtures and solutions of doped oxide or a solution of ingredients which produces a doped oxide film. The various liquid doping compositions are painted, sprayed, spun on or centrifuged onto the semiconductor substrate. Among the liquid doping compositions disclosed in the prior art for fabrication of semiconductor devices are:
(1) U.S. Pat. No. 2,794,846 (Fuller) which discloses use of a glass-like slurry containing mixtures of pulverized particles with an active impurity such as aluminum oxide, with a heat-depolymerizable binder in a solvent;
(2) U.S. Pat. No. 3,084,079 (Harrington) which discloses use of liquid heat-depolymerizable polymers containing a homogeneous mixture of trimethoxyboroxine and methyltrimethoxysilane;
(3) U.S. Pat. No. 3,514,348 (Ku) which discloses use of a liquid dispersion containing colloidal silica particles suspended in water and aqueous solution of a semiconductor dopant such as HBO.sub.3 ; and
(4) U.S. Pat. Nos. 3,658,584 and 3,660,156 (Schmidt) disclose use of colloidal dispersions of a solid copolymer of hydrated silica and a hydrated oxide of a dopant element homogeneously dispersed in an aqueous polar or anhydrous polar solvent, respectively.
The use of the above-described liquid doping composition has introduced additional problems. For example, many of these liquids are incapable of producing thin films or thin films free of pin holes through which contaminants penetrate to degrade surface properties of the semiconductor. Even colloidal silica particles coated with an oxide of a dopant element or glass-like slurry containing mixtures of pulverized particles with aluminum oxide are inadequate to produce continuous doping films which are smooth, uniform and free of pin holes. Other disadvantages of these prior art liquid doping compositions include a non-homogeneous distribution of the dopant agent or the reactivity of components thereof, e.g., alkali metals, free water, carbonaceous decomposition products with the semiconductor substrate, resulting in problems such as nonadherence of the doping film, surface degradation, imperfections, irregular diffusion profiles, low yields, and degradation of electrical properties. A particularly troublesome characteristic of these liquid doping compositions is the tendency to settle, gel, solidify rapidly or degrade, resulting in a short shelf life and requiring use within a few hours or a few days after preparation. Thus, commercial use of these liquid doping compositions has been impeded by practical difficulties in formulating a suspension or solution which is sufficiently stable, sufficently pure, and which can be formulated with sufficient reproducibility from batch to batch.
The prior art also discloses production of junction-type semiconductor devices by applying to a semiconductor substrate, e.g., a wafer, a prefabricated film that serves as a source of dopant. Thus, U.S. Pat. Nos. 3,630,793 and 3,971,870 (Christensen et al.) disclose preparation of a prefabricated film consisting of finely divided dopant such as phosphorus pentoxide or boron nitride homogeneously admixed with a volatile organic binder such as cyanoethylated cellulose. However, if the film applied to the wafer is fired in stacks, as required in any commercial operation, adhesion-preventing agents such as alumina must be included in the mixture or interspersed between the wafers comprising the stacks before the firing operation.
Prefabricated films are also disclosed in U.S. Pat. Nos. 3,915,766 and 3,914,138.
A. M. Litman et al. (Soc. Plast. Eng., Tech. Pap., 1976 Vol. 22, pages 549-551) disclose that 50-70 volume percent of mixtures of ceramic powders, e.g., 85 weight percent silicon nitride, plus 15 weight percent ceria in 30-50 volume percent of polyolefin resin binders are injected molded at an elevated temperature and pressure.